The disclosures herein relate generally to a method and apparatus for identifying the vibration level of CD-ROM discs and more particularly to identifying a speed at which a CD can operate without noticeably vibrating and subsequently identifying that CD each time it is used so that the CD is automatically operated at that speed.
With the advent of faster and faster CD ROM drives, which are attaining speeds of 10.times., 12.times., and faster, vibration and noise from the use of unbalanced or warped CDs has become more pronounced. Such vibration can be caused by CDs which are out-of-round and thus vibrate from the eccentric effect of uneven forces directed radially coincident with the plane in which the CD spins. Vibration from warped CDs causes a wobble effect of uneven forces directed axially and substantially coincident with the spin axis of the CD.
In the normal spin-up of a CD-ROM disc, the disc is inserted into the appropriate slot in the computer and spun-up to 1.times. to read the table of contents. The disc is automatically identified as either an audio (i.e. music) or data disc. If it is an audio disc it is operated at 1.times. which is a speed which would not cause noticeable vibration even if the disc was unbalanced or warped. If it is a data disc it spins up to the maximum speed of the drive which is often 8.times. or faster. At this speed, vibration due to warped or unbalanced discs is not only noticeable but can cause data to be mis-read.
The use of CDs manufactured to less than exacting standards can result in such vibration and noise. Present manufacturing specifications call for the manufacture of CDs to be used with drives running at 1.times. and 2.times.. At these speeds, vibration and noise are not as pronounced. Also, in the past, faster CD ROM drives were available only for desktop computers where vibration is less noticeable due to the relatively larger size of the desktop units, i.e., more damping mass.
Now, faster CD ROM drives are being introduced into the portable PC market. However, the relatively smaller, lighter weight laptop portable units, i.e., notebooks as they are known, have less damping mass than the desktop size units and thus provide little room to implement vibration damping measures. Also, due to the nature of notebook computer use, the unit is often placed on the users lap where vibration is even more noticeable and can be quite annoying.
One method has been developed for testing CD Rom discs for vibration. That method measures laser head movement and thus determines the vibration level of a disc. When vibration is too great, the speed is reduced to a level where vibration is not noticeable. However, each time a disc is to be used, whether it is a disc being used for the first time, or a disc that has been previously tested, the disc must be tested for vibration and the speed reduced if necessary. There is no known method for identifying previously tested discs and automatically setting the correct speed for that disc at which no noticeable vibration will occur.
Therefore, what is needed is a method and apparatus for reading and storing speed data at which a particular CD can operate without noticeable vibration, by testing the CD and subsequently enabling a user to access the data to repeatedly operate the previously tested CD at the speed at which the CD will not noticeably vibrate.